Chromatography Forum

Hey guys.

I´m having trouble with a RID USP technique.
Conditions:
MP: Acetonitrile:Water (79:21)
Flow 2 mL/min
Teperature between 20 - 25 +/- 2 ºC
Column: L8 250 x 4.6 5 um
Working in an Agilent 1100
The problem I have is when I pump through the column. Lot of noise. Pressure is stable, temperature too. Left stabilizing all night and the problem persists. When you put a conector instead the column, noise dissapears, and does the same when turned pump of. No drift.
I´ve tried different columns, but the problem is the same. Tried to clean the cell, and passed Isopropanol because I suspected bubble prescence at first, but nothing.
What could be happening? Any useful advice?

How do you degass your mobile phase?
On the outlet of your RID please connect a short capillary, lets say 20 - 30cm max but check the back pressure, that should avoid that on a column you will get micro bubbles and in the detector cell. Good luck.

Degasser on-line.

Degasser on-line.

Hi,
I think that first solution - special degasser procedure of solvents, before hplc experiment. Please use ultrasonic bath or other procedures for this. Second recommendation - only isocratic mode, from the one bottle.

Thank you

Already did that. And I´m using only channel A.

Hello

Do not check pressure/baseline with zero volume connector (it doesn't generate sufficient backpressure so it will tell you nothing). Try restriction capillary instead or small diameter capillary (backpressure at least 100bar).
I would also check:
-capillary between column and detector - perhaps it is too wide so try one with smaller diameter.
-pump valves (leak test)
-optical unit/RI cell temperature (set it to 40deg)

Best regards

Tomasz Kubowicz

Second recommendation - only isocratic mode, from the one bottle.

Already did that. And I´m using only channel A.

FYI - always purge ALL channels even if you only are using one or two.

Also, when we do RID or conductivity detector, even though isocratic, we always bypass the 1100 MCGV (multi-channel gradient valve) to get a smoother baseline. Agilent has a little adapter part for that, included with a new instrument, looks much like a tan fingertight column nut (Agilent Technologies #0100-1847).

I´m by-passing the multi gradient.

Route the waste and recycle tubing to an upper position , around half a meter, for Agilent RID.
This is recommended by Agilent.